Bacillus subtilis is not only subjected broadly to molecular biological studies as a Gram-positive bacterium model, but it is also used broadly in fermentation-related industries, the pharmaceutical industry, and the like, as a bacterium producing various enzymes such as amylase and protease. The entire nucleotide sequence of Bacillus subtilis genome has already been determined by the joint Japanese and European genome project. However, identification of the functions of approximately 4100 types of gene existing in the Bacillus subtilis genome has not yet been completed.
Strains having approximately 4100 types of disrupted gene existing in the Bacillus subtilis genome have been extensively studied to date. It has thus been suggested that 271 genes are essential for the growth (K. Kobayashi et al., Proc. Natl. Acad. Sci. U.S.A., 100, 4678-4683, 2003).
Furthermore, bacterial strains have each been constructed by deletion or inactivation of a gene involved in early spore formation of Bacillus subtilis or the like or a protease gene, a gene involved in D-alanine addition to teichoic acid within cell walls or cell membranes, or a gene involved in biosynthesis or secretion of Surfactin (see JP Patent Publication (Kokai) No. 58-190390 A (1983), JP Patent Publication (Kokai) No. 61-1381 A (1986), International Publication No. 89/04866 Pamphlet, JP Patent Publication (Kohyo) No. 11-509096 A (1999), JP Patent No. 321.0 315, JP Patent Publication (Kohyo) No. 2001-527401 A, JP Patent Publication (Kohyo) No. 2002-520017 A, and JP Patent Publication (Kohyo) No. 2001-503641 A). However, the degrees of improvement in protein productivity of these bacterial strains have been insufficient. Furthermore, no useful findings have been obtained to date concerning Bacillus subtilis-derived mutant strains having improved productivity of various proteins, or concerning extensive analysis of the mutant strains.